1. Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) device, in particular an out-of-plane sensor, and a method for making the MEMS device, which are less affected by the stress caused by the manufacturing process.
2. Description of Related Art
An out-of-plane sensor senses the capacitance variation resulting from a change of the distance between two electrodes, and generates a corresponding signal. Such out-of-plane sensor may be used in, e.g., an accelerometer. Related art can be found in, e.g., U.S. Pat. Nos. 6,402,968; 6,792,804; 6,845,670; 7,138,694; and 7,258,011.
The above-mentioned prior art discloses either single-capacitor structure occupying a large area, or differential capacitor structure made by wafer bonding. The former consumes too much area, while the latter requires a complicated process that is not compatible with standard CMOS process.
U.S. Pat. Nos. 7,202,101; 7,109,038; 6,622,368; 7,049,051; and 6,936,524 disclose micro-acoustical sensors. Such sensors also require capacitors formed by a plate of a large area. Such large area is vulnerable to stress caused by the manufacturing process.
Therefore, it is desired to provide a MEMS device which can be manufactured by standard CMOS process and less affected by the stress caused by the manufacturing process.